With the development of display technology, flat-panel display devices have replaced heavy CRT display devices and become the mainstream display devices at present. Currently, common flat-panel display devices comprise LCD (Liquid Crystal Display) devices and OLED (Organic Light-Emitting Diode) display devices.
OLED, as a light-emitting device, uses a solid organic semiconductor as luminescent material, and an OLED display device is a display device using the OLED to achieve image display. Particularly, white OLED (i.e., WOLED) technology is the most mature, and WOLEDs, due to the advantages of good stability and simple fabricating process, have been widely used in display devices. In general, a WOLED display device includes an array substrate and a color filter substrate. A plurality of thin film transistors arranged in an array are included in the array substrate, and the thin film transistors serve as control components determining whether light can pass or not. The color filter layer is the key component for the WOLED display device to achieve color display. In fabricating a WOLED display device, generally, the color filter substrate and the array substrate are manufactured separately, and then are aligned and assembled. To guarantee normal operation of a display panel, the alignment and assembly of the array substrate and the color filter substrate require high precision.
With the advances in display technology, at present, a display panel having a structure in which a color filter layer is arranged on an array substrate (Color Filter on Array, and COA for short) to realize color display is used in the WOLED display device. That is, the thin film transistor array and the color filter layer are fabricated on a same substrate, and the color filter layer is provided above the thin film transistor array. FIG. 1 illustrates an example of a WOLED display device with a COA structure formed on a substrate by using a patterning process, in which a planarization protective layer is coated on the color filter layer after the color filter layer is formed, and then a WOLED device (comprising an anode, a light-emitting layer and a cathode) is formed. Specifically, on an array substrate with a thin film transistor (mainly comprising a gate 21, a gate insulation layer 22, an active layer 23, and a source 24 and a drain 25 formed in the same layer) formed thereon, a passivation (PVX) layer 3 is formed by using a patterning process (comprising steps of coating, exposing, developing, and the like), and then a black matrix 4 and a color filter layer 5 are sequentially formed on the passivation layer 3; after that, a resin layer 10 is formed on the color filter layer 5, a metal anode 11 connected to the drain 25 of the thin film transistor is formed on the resin layer 10, then a pixel define layer (PDL for short) 7 and a light-emitting layer (EL for short) 6 are further formed, finally, a metal cathode 12 is formed by sputtering, and a WOLED display device is formed after packaging. The resin layer 10 facilitates improving aperture ratio of the display device, so than an effective pixel area can be increased; meanwhile, logic power consumption is reduced, which greatly reduces power consumption of the product and improves performance of the product.
By using the above display panel with a COA structure, manufacturing of a separate color filter substrate can be omitted, and it is unnecessary to consider the precision of alignment and assembly of the array substrate and the color filter substrate; moreover, the fabricated display panel has better stability and facilitates implementing a large-sized OLED display device, and thus is commonly used in the WOLED display device to realize true color. However, such display panel has complex structure and more manufacturing processes, and requires high-precision matching between the thin film transistor array and the color filter layer, and therefore, it is difficult to achieve a high product yield. In addition, in the process of fabricating an anode by using ITO (Indium Tin Oxide), ITO is deposited on the color filter layer. As the color filter layer has a relatively large thickness, a large level difference is formed, However, ITO is generally thin, and therefore, it is difficult to deposit the ITO layer and breakage in ITO easily happens, which not only results in increased cost of a WOLED display device with such structure, but also decreases product yield.